Rotating, locking intervertebral disk stabilizer and applicator

ABSTRACT

A middle expanded, removable disk implant for stabilizing adjacent vertebrae. The implant is substantially rectangular in cross-sectional shape with a minimal height and a width greater than the height. The implant is detachably mounted to an applicator for insertion into the anatomical region between two adjacent vertebrae from which a portion of the intervertebral disk has been removed. Once inserted, the implant is positioned by anterior-posterior movement in the disk space to the position in which both the expanded, larger width middle portion and the smaller diameter end portions of the implant engage the bodies of the adjacent vertebrae and the implant is then rotated to bring the sides of the rectangularly-shaped implant defining the width of the implant, with its larger dimension, into engagement with the bodies of the adjacent vertebrae. A lock is then secured to the implant to prevent further rotation thereof.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of application Ser.No. 08/900,174 filed Jul. 25, 1997 and entitled ROTATING, LOCKING,INTERVERTEBRAL DISK STABILIZER AND APPLICATOR, now issued as U.S. Pat.No. 5,893,890. Ser. No. 08/900,174 was itself a continuation-in-part ofapplication Ser. No. 08/475,211, filed Jun. 7, 1995 and entitledROTATING LOCKING MIDDLE-EXPANDED INTERVERTEBRAL DISK STABILIZER nowissued as U.S. Pat. No. 5,658,336. Ser. No. 08/475,211 was acontinuation-in-part of International Application No. PCT/US95/03347entitled MIDDLE EXPANDED, REMOVABLE, INTERVERTEBRAL DISK IMPLANT ANDMETHOD OF LUMBAR INTERVERTEBRAL DISK STABILIZATION filed on Mar. 17,1995. International Application No. PCT/US95/03347 was itself acontinuation-in-part of Ser. No. 08/210,229, filed Mar. 18, 1994 andhaving the same title now issued as U.S. Pat. No. 6,093,207.

BACKGROUND OF THE INVENTION

The present invention relates to an intervertebral disk stabilizingimplant for stabilizing two adjacent vertebrae. More specifically, thepresent invention relates to rectangularly-shaped disk implants whichare expanded in the middle portion and are used for spinal fusion.

Treatment of a herniated disk in the neck and in the lumbar regioncontinues to be a challenging field of medicine. The classical treatmentfor a ruptured disk is diskectomy, i.e., removal of the disk frombetween the vertebrae. In this process, all or a portion of theintervertebral disk is removed, leaving a defect which continues tobother the patients throughout the rest of their lives. An additionalprocedure is to replace the disk space with a bone graft, usually bonechips cut from the patient's iliac crest, bringing about fusion of thevertebrae above and below the disk, eliminating the empty space betweenthe vertebrae.

Diskectomy with fusion is not ideal because the replaced bone does nothave the function of the cartilaginous tissue of the disk, i.e. nocushioning effect, and has complications because of several factors.First, conventional bone plugs used to pack the disk space do notconform to the space of the disk because the disk bulges maximally inthe center. The disk space is wider in the middle and narrower at itsanterior and posterior ends. For this reason, the various bone plugswhich are currently available commercially have only four contactpoints, i.e. at the front and back of the disk space. Secondly, accessto the disk is from the side of the dorsal spine of the adjacentvertebrae, leaving a space that is “off-center” relative to the bodiesof the adjacent vertebrae such that the stability of the implant is evenmore problematical than might be apparent from the limited contactresulting from the shape of the intervertebral space. Anothercomplication is the possibility of infection or other conditions whichmay require the removal of the implant. Also, if the bone pieces do notfulse, they may eventually extrude out of the disk space, causingpressure on the nerve roots.

Various prosthetic disk plugs, or implants, are disclosed in the art,but all are characterized by limitations of not conforming to the shapeof the disk space, lack of stability when inserted off-center, inabilityto be removed, or other disadvantages. For instance, U.S. Pat. No.4,863,476 (and its European counterpart, EP-A-0260044) describes anelongated body divided longitudinally into two portions having a camdevice movable therebetween for increasing the space between the twobody portions once inserted into the disk space. However, that device isgenerally cylindrical in shape such that the only contact points betweenthe device and the vertebral bodies are at the front and back of thedisk space, creating increased likelihood of instability and generallyrendering that device unsuitable for use after partial diskectomy. Theart also discloses intervertebral disk prostheses (e.g., U.S. Pat. Nos.3,867,728, 4,309,777, 4,863,477 and 4,932,969 and French PatentApplication No. 8816184) which may have more general contact with theadjacent disks, but which are not intended for use in fusion of thedisks. The art also includes spinal joint prostheses such as isdescribed in U.S. Pat. No. 4,759,769, which is again not indicated foruse when fusion is the preferred surgical intervention.

There is, therefore, a need for a device capable of stabilizing thevertebrae adjacent an intervertebral disk, but which is also removable,for use in spinal fusion. There is also a need for a method ofimplanting such a stabilizer.

SUMMARY OF THE INVENTION

These needs are met in the present invention by providing a vertebraldisk stabilizer comprising an elongate implant having fan, second, thirdand fourth sides providing the implant with a substantially rectangularcross-sectional shape of minimal height defined by the first and secondsides and maximal width defined by the third and fourth sides, the thirdand fourth sides being arched from one end of the implant to the otherto provide the portion intermediate the ends with a width larger thanthe width of the implant at the ends thereof. A lock having a bearingsurface formed thereon is detachably mounted to one end of the implantto prevent rotation of the lock relative to the implant with the bearingsurface oriented at approximately 90° to the height of the implant

A key is formed on the lock and a keyway is formed on the implant forreceiving the key therein. The opening of the keyway is wider than thewidth of the key to facilitate insertion of the key therein. The implantis inserted into the disk space with the implant oriented so that thefirst and second sides thereof engage the bodies of the adjacentvertebrae, rotated approximately 90° in the disk space so that the thirdand fourth sides contact the bodies of the adjacent vertebrae, and thelock is secured to the implant by inserting the key into the keyway toprevent rotation of the implant relative to the lock. The bearingsurface bears against the body of the adjacent vertebrae to preventrotation of the lock relative to the body of the adjacent vertebraeagainst which the surface of the lock bears.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral view of a portion of a human spinal column having apreferred embodiment of vertebral disk stabilizer of the presentinvention inserted therein and having a portion of the bodies of thevertebrae adjacent the implant shown cut away and/or in shadow lines toshow the engagement of the vertebral bodies by the vertebral diskstabilizer.

FIG. 2 is an exploded, perspective view of the vertebral disk stabilizerof FIG. 1.

FIG. 3 is a view of the implant of FIG. 1 and an applicator to which theimplant can be mounted in place of the lock shown in FIG. 2, the implantbeing shown in side, elevational view and the applicator being shown intop, plan view.

FIG. 4 is an exploded, perspective view of a second preferred embodimentof the vertebral disk stabilizer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures, a first embodiment of a disk stabilizerconstructed in accordance with the teachings of the present invention isshown implanted in a human spinal column in FIG. 1. The vertebral diskstabilizer, indicated generally at reference numeral 10, is implantedbetween the bodies 12 and 14 of two adjacent vertebrae 16 and 18,respectively, in the disk space (not numbered) from which a portion ofthe intervertebral disk 20 is removed, i.e. by simple diskectomy andsmall laminotomy.

Referring now also to FIG. 2, the vertebral disk stabilizer 10 iscomprised of an elongate implant 22, lock 24, and means for detachablymounting the lock 24 to one end 25 of the implant 22. In the presentlypreferred embodiment shown, the mounting means takes the form of a bolt26 passing through a bore 28 in lock 24, the threads of bolt 26 engagingcomplementary threads in the walls of the bore 30 in the end 25 ofimplant 22. A lock nut 31 may optionally be provided for resisting theloosening of the bolt 26 once lock 24 is mounted to lock 24 and implant22 in the manner described below.

In more detail, implant 22 is comprised of first and second sides 32 andthird and fourth sides 34 providing a substantially rectangularly shapedcross-section. The height H of the rectangularly shaped cross-section isdefined by first and second sides 32 and the width W is defined by thethird and fourth sides 34 and, as is apparent by comparison of H and W,the height of H of implant 22 is less than the width W. As will beexplained below, H is minimized to facilitate insertion of the secondend 36 into, and positioning of implant 22 in, the disk space from whicha portion of the intervertebral disk 20 was removed and W is maximizedto provide the desired stabilization to adjacent vertebrae 16 and 18.Third and fourth sides 34 are arched from one end of implant 22 to theother to provide the portion of implant 22 intermediate the ends 25 and36 with a width W which is larger than the width W′ and W″ at the ends25 and 36, respectively. By comparison of the widths at the ends andmiddle portions of implant 22, it can be seen that in the embodimentshown in FIG. 2, the width W′ at the end 25 of implant 22 is less thanthe width W″ at the end 36 of implant 22. Because the sides 32 ofimplant 22 are substantially flat and the sides 34 are arched from oneend 25 to the other end 36, implant 22 is described as being abi-planar, bi-convex implant The bi-convex sides 34 of implant 22 areprovided with a plurality of teeth 38 for biting into the adjacentvertebrae 16 and 18 as will be explained in more detail below. The end36 of implant 22 is formed in a blunt, or rounded shape to reduce thelikelihood of injury to the nerves of the spinal cord during insertioninto the disk space.

Those skilled in the art who have the benefit of this disclosure willrecognize from the preceding paragraph that the sides 34 of implant 22need not define an arch which is symmetrical from the end 25 to the end36 of implant 22. It will also be recognized that the sides 34 ofimplant 22 need not be provided with the serrations 38 to bite into theadjacent vertebrae. This biting function can also be accomplished byproviding the sides 34 with multiple steps formed in right angles fromthe narrowest portions at the ends 25 and 36 to the widest portion inthe approximate middle of implant 22 (i.e., from the dimension W′ to Wto W″).

In the preferred embodiment shown, lock 24 is substantially square whenviewed from the end 40 along the axis of the bore 28 therethrough andU-shaped when viewed from the side. The inside surfaces 42 of the arms44 of the U-shaped lock 24 are flat for contacting the first and secondsides 32 of implant 22 to prevent rotation of lock 24 relative toimplant 22 when lock 24 is mounted to implant 22 and secured thereto bybolt 26. The sides 32 of implant 22 are provided with a keyway 46 forreceiving complementary-shaped keys 48 formed on the surfaces 42 of thearms 44 of lock 24 to facilitate assembly of lock 24 to implant 22;those skilled in the art who have the benefit of this disclosure willrecognize that the keyway 46 may be located on the lock 24 and the key48 may be located on implant 22 without any difference in the manner inwhich those component parts function. The mouth 45 of the keyway 46 onthe side 32 of implant 22 at the first end 25 of the implant is widerthan the width of the keyway 46 in the portion of the slot intermediatethe ends 25 and 36 of implant 22 to facilatate insertion of the keys 48of lock 24 into the keyway 46. The funnel-shaped portion 47 of thekeyway 46 behind the mouth 45, which gradually decreases in width, actsto increase the ease with which lock 24 is mounted to implant 22 byinsertion of the keys 48 into the respective keyways 46 and helps toseat lock 24 thereon and align the bore 28 in lock 24 with the bore 30in implant 22.

The sides of the square end 40 of lock 24 provide surfaces 50 forbearing against the bodies 12 and 14 of adjacent vertebrae 16 and 18 asalso explained in more detail below. It will be recognized by thoseskilled in the art who have the benefit of this disclosure that thebearing surfaces 50 need not be flat and that the end 40 of lock 24 neednot be square. Other shapes and configurations may be utilized as neededto insure that movement of lock 24 is limited by the bodies of theadjacent vertebrae 16 and 18. The purpose of the bi-planar, middleexpanded, bi-convex implant 22 is to enable insertion of the implant 22into the disk space and turning by approximately 90° to increase thedisk height and stabilize the disk space. The purpose of lock 24 is tolock implant 22 against instability when in the vertical position so asto maintain the disk height thereafter.

Referring now to FIG. 3, an applicator for use in connection with thepresent invention is shown at 152 and is provided with an end 154 shapedin the form of a pair of prongs 144. The prongs 144 are formed in a sizeand shape substantially identical to the size and shape of the arms 44of lock 24. Applicator 152 is mounted to implant 22 by inserting theprongs 144 into the keyways 46 formed on the sides 32 of implant 22(note that implant 22 must be rotated by 90° from the position shown inFIG. 3 to be mounted on applicator 152, the implant 22 and applicator152 being shown in the relationship shown in FIG. 3 to show thestructure which enables the implant to be mounted to the applicator). Inthis manner, the prongs effectively function in the manner of the keys48 formed on the surfaces 42 of the arms 44 of lock 24, seating theimplant 22 on the end of applicator 152 and preventing relativerotational movement between implant 22 and applicator 152. Although notshown in the figure, those skilled in the art who have the benefit ofthis disclosure will recognize that the end of the keyways 46 may beextended along the sides 32 of implant 22 further than is necessary toreceive the keys 48 on lock 24 and that the extra length of the keyways46 may be of gradually reducing dimension so that the prongs 144 ofapplicator 152 are received in a friction fit in the keyways 46 to helpaffirmatively mount implant 22 thereto. Other structure for achievingthis same result includes a detent or serrations formed in the keyways46.

When the end 154 of applicator 152 is seated all the way into thekeyways 46 of implant 22, so as to prevent relative rotational movementtherebetween, implant 22 is inserted into the disk space and rotatedtherein using applicator 152 as explained below. Applicator 152 is thendetached from implant 22 simply by withdrawing the applicator 152 fromthe disk space, the friction exerted by the adjacent vertebraepreventing the withdrawal of the implant 22. It will be apparent tothose skilled in the art who have the benefit of this disclosure thatthe applicator 152 is of little assistance in removing the implant 22from the disk space even if the keyways 46 of implant 22 are providedwith a detent or other structure to engage the prongs 144 of applicator152 to retain the implant 22 thereon. In the event the implant 22 needsto be removed from the disk space, an applicator of the type shown in myprior, U.S. Pat. No. 5,658,336, which disclosure is incorporated in itsentirety as if fully set forth herein by this specific referencethereto, is screwed into the bore 30 to allow the implant 22 to bepulled from the disk space.

A second embodiment of the implant of the present invention is shown inFIG. 4. In this second embodiment, the structure corresponding to thestructure of the embodiment shown in FIGS. 1-3 is designated with aprime to distinguish between the two embodiments. The arms 44′ of lock24′ are shaped so that the arms 44′ themselves provide the keys 48′which fit into the complementary-shaped keyways 46′ on the surfaces 32′of implant 22′. Specifically, the arms 44′ forming the U-shaped lock 24′are shaped in the form of prongs which fit into the keyways 46′ ofimplant 22 in much the same manner as described for the prongs 144 ofthe applicator 152 shown in FIG. 3. In this manner, the lock 24′functions in the same manner as the lock 24 of FIGS. 1-3 to preventrotation of implant 22′ once inserted into the disk space and rotated byapproximately 90°.

The use of the stabilizer 10 of the present invention in, for instance,a method of lumbar intervertebral disk stabilization is illustrated inFIG. 1. Surgery is performed as in a simple diskectomy and theintervertebral disk 20 is exposed through a small laminotomy. The diskmaterial is removed and any nerve root compression is corrected. Theposterior longitudinal ligament (not shown) and disk cartilage areremoved until the surface of the bodies 12 and 14 of adjacent vertebrae16 and 18, respectively, are exposed above and below the disk space.

Using spreaders such as those disclosed in my International ApplicationNo. PCTI/US95/00347, which reference is hereby incorporated into thisspecification in its entirety by this specific reference thereto, thevertebrae 16 and 18 are distracted to open the disk space, and once thedesired “spread” is achieved, the middle portion of the disk space ispacked with cancellous bone chips (not shown). Because the posteriorlongitudinal ligament is left intact to the opposite side and to thecenter of the disk space, the bone chips are held in place in the diskspace.

An implant 22 having a height H and width W selected to fit the diskspace is then mounted to the prongs 144 of applicator 152. Theappropriately-sized implant 22 is then inserted into the disk spaceusing the applicator 152 with the implant 22 oriented so that the topand bottom thereof, i.e., the first and second sides 32, engage thebodies 12 and 14 of adjacent vertebrae 16 and 18, respectively. Usingthe applicator 152, implant 22 is positioned in the disk space at aposition in which the expanded, middle portion and the smaller widthends 25 and 36 of the third and fourth sides 34 of implant 22 contactthe respective lower and upper surfaces of the bodies 12 and 14 of theadjacent vertebrae 16 and 18 when rotated by approximately 90° using theapplicator 152. The respective lower and upper surfaces of the vertebralbodies 12 and 14 are slightly concave such that the larger width middleportion W″ of implant 22 allows the implant 22 to engage substantiallymore of the respective surfaces of the vertebral bodies 12 and 14 thanconventional prosthetic devices, thereby providing increased stabilityto the fusion once further rotation of implant 22 in the disk space isprevented as described below.

Once positioned in the disk space so as to provide maximumstabilization, the applicator 152 is then detached from the implant 22by backing out of the incision in the patient. Lock 24 is then insertedthrough that same incision and, using the slot 46 and key 48, the bore28 in lock 24 and bore 30 in implant 22 are aligned and the bolt 26 isinserted and tightened to secure lock 24 to the implant 22. Securing thelock 24 to implant 22 in this manner prevents relative rotation betweenlock 24 and implant 22 and the bearing surfaces 50 of lock 24 bearagainst the bodies 12 and 14 of the adjacent vertebrae 16 and 18 toprevent rotation of the lock 24 relative to the adjacent vertebrae 16and 18 against which the bearing surfaces 50 bear. Those skilled in theart who have the benefit of this disclosure will recognize that thebearing surfaces 50 bear against the cortical end plate of therespective vertebral bodies 12 and 14, which is comprised ofnon-cancellous bone, and provides a hard, relatively smooth surfaceagainst which the bearing surfaces 50 bear. The end 40 of lock 24 ispreferably supplied in a plurality of different sizes and shapes otherthan the square shaped end 40 shown in the figures so as to allow thesurgeon to select an appropriately sized and shaped lock which providesa close fit with the space between vertebral bodies.

If necessary, a small amount of a physiologically compatible adhesive ofa type known in the art is applied over the cancellous bone chips justmedial to the implant to close off the remaining portion of the openinginto the disk space. The patient should be able to ambulate soon afterthe procedure because of the stability imparted to the spinal column bythe implant of the present invention. Before narrowing of the disk spaceoccurs, the cancellous bone chips will have started the fusion process.

The stabilizer 10 is also used to advantage to perform, for instance, aposterior lateral intertransverse fusion. The implant 22 is insertedinto the region of the disk space from which a portion of the disk hasbeen removed as described above with the lock 24 and the posteriorlateral fusion performed. Because the implant 22 provides stability tothe spine until the posterior lateral fusion is solid, the patient isgenerally able to ambulate soon after surgery. This procedure alsoprevents the narrowing of the disk space, which is a common problem withposterior lateral fusion.

Removal of the implant 22 is accomplished with relative ease compared toconventional implants. The bolt 26 is screwed back out of implant 22 andlock 24 is pulled out of the disk space. An applicator of the typedescribed in the above-incorporated Ser. No. 08/475,211 is inserted intothe disk space and screwed into the bore 30 in implant 22 and used torotate implant 22 by approximately an additional 90°, causing the firstand second sides, having minimal height, to contact the bodies 12 and 14of adjacent vertebrae 16 and 18 so as to allow posteriorly-directedmovement of the implant 22 out of the disk space.

Although described in terms of the preferred embodiment shown in thefigures, this embodiment is shown to exemplify the present invention, itbeing recognized by those skilled in the art that certain changes can bemade to the specific structure of the preferred embodiment shown anddescribed without departing from the spirit of the present invention. Inthe case of one such change, the first and second sides of the implantare substantially flat but not parallel along their longitudinal axes sothat the implant is wedge-shaped. The wedge shape of the implantfacilitates insertion of the implant into the disk space, the roundedend of the implant reducing the likelihood of injury to the nerves ofthe spinal cord during insertion into the disk space. Likewise, thewidth at one end of the implant can be less than the width at the end,both widths, however, being less than the width in the middle, expandedportion of the implant. Further, the connection by which lock 24 ismounted to implant 22 is capable of being constructed in a mannerdifferent than that shown in the figures herein. Another such implantinto the disk space, the rounded end of the implant reducing thelikelihood of injury to the nerves of the spinal cord during insertioninto the disk space. Likewise, the width at one end of the implant canbe less than the width at the end, both widths, however, being less thanthe width in the middle, expanded portion of the implant. Further, theconnection by which lock 24 is mounted to implant 22 is capable of beingconstructed in a manner different than that shown in the figures herein.Another such modification relates to the teeth 38 formed on the sides 34of implant 22. So as to provide additional resistance to forward orbackward movement of implant 22 in the disk space, the teeth 38 locatedclosest to the end 25 of implant 22 (e.g., the teeth in the distalportion of implant 22) may be oriented at a slant toward the end 25 andthe teeth 38 closest to the end 36 of implant 22 may be oriented at aslant toward the end 36. The teeth in the middle portion of implant 22,e.g., between the two sets of slanted teeth, are then orientedvertically. All such modifications, and other modifications which do notdepart from the spirit of the present invention, are intended to fallwithin the scope of the following claims.

What is claimed is:
 1. A stabilizer for implanting in the disk spacebetween adjacent vertebrae of a patient to stabilize the vertebraecomprising: an elongate implant having a substantially rectangularcross-sectional shape with a minimal height defined by first and secondsides and a maximal width defined by third and fourth sides, the thirdand fourth sides being arched from one end of the implant to the other;a lock defining a bearing surface; a bolt for mounting said lock to oneend of said implant to resist rotation of said implant in the disk spacewhen said implant is inserted into the disk space and rotated so thatthe third and fourth sides of said implant and the bearing surface ofsaid lock contact the adjacent vertebrae; a key formed on said lock; anda keyway formed on said implant for receiving said key therein, saidkeyway having a mouth wider than the width of said key for facilitatinginsertion of said key therein.
 2. The stabilizer of claim 1 wherein saidkeyway is provided with a funnel-shaped portion behind the mouth, thewidth of the funnel-shaped portion decreasing to the width of saidkeyway.
 3. The stabilizer of claim 1 wherein both the first and secondsides of said implant are provided with said keyways.
 4. The stabilizerof claim 3 wherein said keyways are provided with funnel-shaped portionsbehind their respective mouths, the width of the funnel-shaped portionsdecreasing to the width of said keyways.
 5. A spinal stabilizer andapplicator comprising: an elongate implant having a substantiallyrectangular cross-sectional shape with a minimal height defined by firstand second sides and a maximal width defined by third and fourth sides,the third and fourth sides being arched from one end of the implant tothe other; a lock detachably mounted on said implant and defining asurface for bearing against the adjacent vertebrae; a bolt for mountingsaid lock to said implant to resist rotation of said implant after saidimplant is inserted into the disk space and rotated so that the thirdand fourth sides of said implant and the bearing surface of said lockcontact the adjacent vertebrae; a key formed on said lock; a keywayformed on said implant for receiving said key therein, said keywayhaving a mouth wider than the width of said key and a funnel-shapedportion of decreasing width; and an applicator for detachably mountingto said implant having prongs formed thereon shaped to fit into thefunnel-shaped portion of said keyway.
 6. The stabilizer of claim 5wherein the prongs of said applicator are flush with the surfaces of thefirst and second sides of said implant when the prongs are engaged tothe funnel-shaped portion of said keyway.
 7. The stabilizer of claim 1additionally comprising a lock nut for preventing the loosening of saidbolt.